Display device

ABSTRACT

A display device includes a plurality of sub-pixels configured to display a plurality of colors including white. Each of the sub-pixels includes a self-luminous element configured to emit light by receiving supply of electric current, an input unit configured to input a luminance signal for determining luminance of the self-luminous element into the sub-pixel, and a control unit configured to control the supply of electric current to the self-luminous element. An area of light emission in each of the sub-pixels for the white is larger than an area of light emission in each of the sub-pixels for the other colors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application P2005-099932 filed on Mar. 30, 2005,and Japanese Patent Application P2005-252699 filed on Aug. 31, 2005; theentire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and, moreparticularly, to a display device including plural colors of sub-pixels.

2. Description of the Related Art

These years, development of organic electroluminescence (EL) displaydevices has been under way. For example, adoption of organic EL displaydevices for mobile phones has been under consideration. Methods ofdriving organic EL display devices include a passive matrix drivingmethod and an active matrix driving method. In the case of the passivedriving method, scan electrodes and data electrodes are used, and thuspixels are driven by time-division; In the case of the active matrixdriving method, thin film transistors (TFTs) are arranged respectivelyin pixels, and thus light emission of respective pixels is heldthroughout one vertical scan time period.

In the case of organic EL display devices, it has been known thatsubstantial luminous efficiencies of organic EL elements respectivelyfor colors are different from one color to another, and that life spansof the organic EL elements are dependent on electric current densitiesapplied respectively to the organic EL elements. With regard to organicEL display devices, a larger electric current has to be applied tosub-pixels with a poorer luminous efficiency than that applied to theother sub-pixels with a better luminous efficiency for the purpose ofobtaining predetermined luminance in each of the sub-pixels with thepoorer luminous efficiency, in a case where all of these sub-pixels havean equal area of light emission. That is because luminous efficienciesof organic EL elements respectively for colors are different from onecolor to another in the aforementioned manner. This brings about aproblem that the elements of the sub-pixels to which the larger electriccurrent is applied become shorter in life span, and another problem thata display device as a whole accordingly becomes shorter in life span.

For the purpose of solving such problems, the following method has beenproposed. In the case of this method, areas of light emission insub-pixels respectively for the colors are different from one color toanother depending on luminous efficiencies thereof. Thereby, sub-pixelsfor any one of the colors have a life span almost equal to those ofsub-pixels for the other colors. (See Japanese Patent Laid-open OfficialGazette No. 2001-290441, for instance)

In addition, a method of expressing videos by use of four colors of red,green, blue and white has been proposed as a method of reducing powerconsumption of organic EL display devices (see Japanese Patent Laid-openOfficial Gazette No. 2004-334204, for instance). Organic EL elements areself-luminous elements. For this reason, organic EL elements start toconsume power when the organic EL elements start to emit light. In otherwords, organic EL display devices display videos by causing individualpixels to emit light. Thus, no sooner do the organic EL display devicesstart to display a video than the power consumption occurs. For thisreason, in the case where videos are expressed by use of the threecolors of red, green and blue, electric current is consumed most whenwhite is displayed by emitting the three colors at a time. To put itanother way, for the purpose of reducing power consumption, it sufficesthat sub-pixels for the three colors are designed not to emit light at atime. With this taken into consideration, videos are designed to bedisplayed by use of four colors which are obtained by adding white tothe three colors. Luminous efficiency of a sub-pixel for white is atleast more than twice as high as substantial luminous efficiency of eachof sub-pixels respectively for red and blue. In addition, white isdesigned to be displayed by causing sub-pixels for white to emit light.Display of white consumes power most among displays respectively of thefour colors. These designs make it possible to check sub-pixels for thethree colors from emitting light, and to accordingly reduce powerconsumption. (see US Patent Published Application No. 20020186214, forinstance)

With regard to conventional organic EL display devices each includingsub-pixels for the three different colors, several types of circuitlayouts have been known. A stripe layout has been known as the mostgenerally-used circuit layout. In the case of the stripe layout,sub-pixels for the colors are arrayed in lines. Scan lines and datalines are provided. The data lines are arranged in a way that the datalines are orthogonal to the scan lines. For the purpose of drivingactive matrix organic EL display devices with the stripe layout, voltageis applied to the scan lines, and thus sub-pixels are selected. Inaddition, luminance levels respectively of the sub-pixels are controlledby use of voltage signals which are stored in the data lines.

A delta layout has been known as a second type of circuit layout. In thecase of the delta layout, sub-pixels are laid out in triangular patternsinstead of in lines. The delta layout makes sub-pixels respectively forthe three colors closer to each other than the stripe layout does. Forthis reason, in many cases, the delta layout provides viewers with moredesirable appearance than the stripe layout does. A method of applyingsuch a circuit layout to organic EL display devices including sub-pixelsfor the four colors has been proposed (see Japanese Patent Laid-openOfficial Gazette No. 2004-334204, for example).

Particularly in a case where organic EL display devices are applied tomobile phones, it is strongly demanded that power consumption should bereduced. For this reason, the method of expressing videos by use of thefour colors of red, green, blue and white, which has been disclosed inJapanese Paten Laid-open Official Gazette No. 2004-334204, is effectivefor the application of organic EL display devices to mobile phones.However, the present inventors have found that, in a case where atechnique disclosed in Japanese Patent Laid-open Official Gazette No.2001-290441 is applied to organic EL display devices which displayvideos by use of the four color of red, green, blue and white, thefollowing problem is brought about. The problem is that life spans ofsub-pixels are different from one color to another in a case where areasof light emission in sub-pixels respectively for the four colors aremade different from one another depending on luminous efficiencies ofthe sub-pixels by applying the technique.

Furthermore, for the purpose of improving visibility of this type oforganic EL display devices using the four colors, consideration needs tobe paid lest sub-pixels should be arranged lopsidedly for each color.

With these conditions taken into consideration, the present inventionhas been made. An object of the present invention is to provide atechnique which enables life span of organic EL display devices to beextended. Another object of the present invention is to provide atechnique which realizes organic EL display devices with a bettervisibility.

SUMMARY OF THE INVENTION

An aspect of the present invention inheres in a display deviceencompassing, a plurality of sub-pixels configured to display aplurality of colors including white, each of the sub-pixels including: aself-luminous element configured to emit light by receiving supply ofelectric current, an input unit configured to input a luminance signalfor determining luminance of the self-luminous element into thesub-pixel, and a control unit configured to control the supply ofelectric current to the self-luminous element, wherein an area of lightemission in each of the sub-pixels for the white is larger than an areaof light emission in each of the sub-pixels for the other colors.

Since an area of light emission in each of the sub-pixels for the white,which greatly consume electric current in displaying images, is largerthan an area of light emission in each of the sub-pixels for the othercolors, it is possible to extend the life span of the display device bysmoothing the life span of the elements.

In the display device according to the aspect, the displayed colors maybe four colors of blue, green, red, and white. The provision of thewhite sub-pixel makes it possible to reduce power consumption.

In the display device according to the aspect, a ratio among thesub-pixels for each of the colors in an area of light emission may beset up in accordance with a ratio among substantial electric currentssupplied to the self-luminous elements for each of the colors. Forexample, the ratio among the electric currents may be calculated fromaverages of electric currents supplied to the self-luminous elementswhen a plurality of images, such as natural images, are displayed on thedisplay device.

Since a ratio among the sub-pixels for each of the colors in an area oflight emission is set up in accordance with a ratio among substantialelectric currents supplied to the self-luminous elements for each of thecolors, it is possible to appropriately smooth the life span of theelements.

In the display device according to the aspect, a color emitted by theself-luminous element is the white, and the other displayed colors maybe obtained by converting the white to the displayed colors except forthe white by use of color filters. It is possible to increase yieldsbecause step of depositing luminous elements can be simplified. It ispossible to increase the resolution because interstices between eachneighboring two of the sub-pixels can be narrower.

Another aspect of the present invention inheres in a display deviceencompassing, a plurality of sub-pixels arranged in horizontaldirection, and configured to display a plurality of colors, and toconstitute an image component, each of the sub-pixels including: aself-luminous element configured to emit light by receiving supply ofelectric current, an input unit configured to input a luminance signalfor determining luminance of the self-luminous element into thesub-pixel, and a control unit configured to control the supply ofelectric current to the self-luminous element, wherein at least twosub-pixels of the sub-pixels have an equal horizontal pitch.

In the display device according to another aspect, at least twosub-pixels of the sub-pixels, which are not next to each other, may havean equal horizontal pitch. In the display device according to anotheraspect, sub-pixels for any one of the colors may be arranged in a waythat the sub-pixels for the same color are not next to each other.

Since two sub-pixels of the sub-pixels, which are not next to eachother, may have an equal horizontal pitch, for instance a delta layout,it is possible to reduce the number of pixel layout patterns, and toreduce a load imposed on layout design.

Still another aspect of the present invention inheres in a displaydevice encompassing, a plurality of sub-pixels arranged in horizontaldirection, and configured to display a plurality of colors, and toconstitute an image component, each of the sub-pixels including: aself-luminous element configured to emit light by receiving supply ofelectric current, an input unit configured to input a luminance signalfor determining luminance of the self-luminous element into thesub-pixel, and a control unit configured to control the supply ofelectric current to the self-luminous element, wherein image componentsnext to each other in vertical direction are arranged in a way that oneof the image components shifts from the other of the image components bya distance equal to a half of a horizontal pitch of each of the imagecomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pixel layout diagram showing an organic EL display deviceaccording to a first embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of any one ofsub-pixels in the organic EL display device shown in FIG. 1.

FIG. 3 is a schematic diagram showing a cross section of the organic ELdisplay device according to the first embodiment.

FIG. 4 is a pixel layout diagram showing an organic EL display deviceaccording to a second embodiment.

FIG. 5 is a pixel layout diagram showing an organic EL display deviceaccording to a third embodiment.

FIG. 6 is a pixel layout diagram showing an example in an active matrixdisplay device.

FIG. 7 is a pixel layout diagram showing an example in an active matrixdisplay device.

FIG. 8 is a schematic diagram showing a case where the sub-pixels shownin FIG. 5 are arranged in the pixel arrangement of FIG. 7.

FIG. 9 is a schematic diagram showing a case where the sub-pixels shownin FIG. 5 are arranged in the pixel arrangement of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described withreference to the accompanying drawings. It is to be noted that the sameor similar reference numerals are applied to the same or similar partsand elements throughout the drawings, and the description of the same orsimilar parts and elements will be omitted or simplified.

First Embodiment

FIG. 1 shows a pixel layout of an organic EL display device according toa first embodiment of the present invention. As shown in FIG. 1, theorganic EL display device 10 according to the first embodiment includesfour color sub-pixels: a sub-pixel A1 for red, a sub-pixel A2 for green,a sub-pixel A3 for blue, and a sub-pixel A4 for white. A constitutionalunit (pixel) 12 is constituted of the four color sub-pixels A1, A2, A3,and A4 which are arranged side-by-side. When the white sub-pixel A4 isprovided to the constitutional (pixel) 12, the lighting of only thewhite sub-pixel A4 is sufficient for the white color to be displayed,instead of the lighting of all of the red, green, and blue sub-pixelsA1, A2, and A3. Accordingly, the provision of the white sub-pixel A4makes it possible to reduce power consumption.

Each of the sub-pixels A1, A2, A3, and A4 is constituted of a powersupply line PVDD1, a gate line SL1, a data line DL1, a storage capacitorline SCL, an organic EL element OEL1, a drive transistor MN2, a writetransistor MN1, and a storage capacitor SC. The drive transistor MN2controls supply of electric current to the organic EL element OEL1. Thewrite transistor MN1 is turned to a conductive state in response toapplication of a selection signal to the gate line SL1, and thus takes aluminance signal for determining luminance of the organic EL elementOEL1 into the sub-pixel. The storage capacitor SC is provided in aninterstice between a gate electrode of the drive transistor MN2 and thestorage capacitor line SCL, and stores data voltage. FIG. 2 is a diagramshowing an equivalent circuit of any one of sub-pixels A1, A2, A3 and A4in the organic EL display device 10 shown in FIG. 1.

FIG. 3 schematically shows a cross section of the organic EL displaydevice 10 according to the first embodiment. As shown in FIG. 3, thethree colors of red, green, and blue are obtained by converting whitelight from an organic EL luminescent layer 17, which is emitting white,to the colors by use of red, green, and blue color filters 16. The whitecolor is obtained by using white light, which is emitted from theorganic EL luminescent layer 17, as it is. The organic EL display device10 displays a full spectrum of color by use of these four colors. Inthis regard, the organic EL luminescent layer 17 emitting white isconstituted of a laminar structure of a luminescent layer emitting blueand a luminescent layer emitting orange. When the four color sub-pixelsare formed of four types of organic EL luminescent layers respectivelyemitting red, green, blue, and white, interstices between eachneighboring two of the sub-pixels have to be set relatively wider whilethe luminescent layers are being deposited by use of a metal mask.Accordingly, this deteriorates resolution. In addition, when the colorsare coated separately, the step of depositing luminous elements has tobe multiplied. Accordingly, this decreases yields. In the case of theorganic EL display device 10 according to the first embodiment, itsuffices that the organic EL luminescent layer 17 is deposited on theentire surface. This makes it possible to preclude the aforementionedproblems, and to accordingly improve the resolution and yields.

With regard to the organic EL display device 10 according to the firstembodiment, a ratio among maximum electric current values required fortheir respective colors to be emitted was calculated by use of effectiveluminous efficiencies and chromaticities of the colors which weremeasured after white light was transmitted through the color filters 16.At this time, the ratio was red:green:blue:white=1.1:1.3:3.5:1.0. From asimulation conducted by the present inventor, however, it has been foundthat, in a case where a plurality of arbitrary natural images, such aslandscape photos and portraits, were displayed, a ratio among averagesof electric currents flowing in the respective organic EL elements OEL1was red:green:blue:white=1.0:1.1:1.1:2.4. As a result, when a ratioamong the four color sub-pixels in luminous area is determined by use ofthe aforementioned ratio among the maximum electric current values, thecurrent density of the white sub-pixel is highest when an actual video,particularly a natural image, is displayed. This is because the area ofthe white sub-pixel to consume electric current most among the fourcolor sub-pixels is smallest. In other words, the white sub-pixel isdeteriorated in the shortest length of time among the four colorsub-pixels. Accordingly, this shortens the life span of the organic ELdisplay device 10 as a whole.

With this taken into consideration, in the case of the organic ELdisplay device 10 according to this embodiment, the luminous area of thewhite sub-pixel A4 is designed to be the largest among the four colorsub-pixels, as shown in FIG. 1. Specifically, a ratio among the fourcolor sub-pixels in area of the opening portion is designed to bered:green:blue:white=1:1:1:2. This ratio makes it possible to reduce theelectric current density of the white sub-pixel which consumes electriccurrent most among the four color sub-pixels although the luminousefficiency of the white sub-pixel is the highest among the luminousefficiencies of the four color sub-pixels. Accordingly, this makes itpossible to reduce deterioration of the organic EL element OEL1 of thewhite sub-pixel A4. In other word, this makes it possible to leveldeterioration speeds of the organic EL elements respectively for thefour colors. In addition, this makes it possible to reduce powerconsumption of the organic EL display device 10.

Second Embodiment

Descriptions will be provided for a second embodiment of the presentinvention. FIG. 4 is a diagram of a pixel layout of an organic ELdisplay device 10 according to the second embodiment. The pixel layoutaccording to this embodiment is different from the pixel layoutaccording to the first embodiment, which has been shown in FIG. 1, interms of the ratio among the red, green, blue and white sub-pixels inarea of the opening portion. This is because organic EL elementsaccording to this embodiment are different from those according to thefirst embodiment.

With regard to the organic EL elements OEL1 according to the secondembodiment, a ratio among maximum electric current values required fortheir respective colors to be emitted was calculated by use of effectiveluminous efficiencies and chromaticities of the colors which weremeasured after white light was transmitted through the color filters 16.At this time, the ratio was red:green:blue:white=1.4:1.1:1.4:1.0. From asimulation conducted by the present inventors, however, it has beenfound that, in a case where a plurality of arbitrary natural images,such as landscape photos and portraits, were displayed, a ratio amongaverages of electric currents flowing in the respective organic ELelements OEL1 was red:green:blue:white=1.0:0.6:1.2:2.3. With this resulttaken into consideration, in the case of the organic EL display device10 according to the second embodiment which has been shown in FIG. 4, aratio among the red, green, blue and white sub-pixels in area of theopening portion is set at 1.0:0.8:1.2:1.7, whereas, in the case of theorganic EL display device 10 according to the first embodiment, theratio among the red, green, blue and white sub-pixels in area of theopening portion is set at 1:1:1:2. In the case of the second embodiment,the white sub-pixel A4 is designed to be the largest in area of theopening portion among the four color sub-pixels as well. Accordingly,this makes it possible to reduce deterioration of the organic EL elementOEL1 of the white sub-pixel A4, and to thus extend the life span of theorganic EL display device 10.

Third Embodiment

Descriptions will be provided for a third embodiment of the presentinvention. FIG. 5 is a diagram of a pixel layout of an organic ELdisplay device 10 according to this embodiment. Like the pixel layoutaccording to the second embodiment, the pixel layout according to thisembodiment is different from the pixel layout according to the firstembodiment in terms of the ratio among the red, green, blue and whitesub-pixels in area of the opening portion. This is because organic ELelements according to this embodiment are different from those accordingto the first embodiment.

With regard to the organic EL display device 10 according to the thirdembodiment, a ratio among maximum electric current values required fortheir respective colors to be emitted was calculated by use of effectiveluminous efficiencies and chromaticities of the colors which weremeasured after white light was transmitted through the color filters 16.At this time, the ratio was red:green:blue:white=1.1:1.1:1.2:1.0. From asimulation conducted by the present inventors, however, it has beenfound that, in a case where a plurality of arbitrary natural images,such as landscape photos and portraits, were displayed, a ratio amongaverages of electric currents flowing in the respective organic ELelements OEL1 was red:green:blue:white=1.0:1.1:1.2:2.4. With this resulttaken into consideration, in the case of the organic EL display device10 according to the third embodiment, a ratio among the red, green, blueand white sub-pixels in area of the opening portion is set at1.0:1.0:1.2:2.0. In this case, the white sub-pixel A4 is designed to bethe largest in area of the opening portion among the four colorsub-pixels as well. Accordingly, this makes it possible to reducedeterioration of the organic EL element OEL1 of the white sub-pixel A4,and to thus extend the life span of the organic EL display device 10.

As described above, with regard to the first to the third embodiment,irrespective of the types of the organic EL elements OEL1, the maximumelectric current value of the white sub-pixel A4 is theoretically thesmallest among those of the four color sub-pixels in the case of each ofthe embodiments. However, the luminous area of the white sub-pixel A4 isdesigned to be the largest among those of the color sub-pixels in thecase of each of the embodiments. In the case of each of the embodiments,such a design makes it possible to reduce the current density of thewhite sub-pixel A4, and to accordingly reduce deterioration of theorganic EL element OEL1 of the white sub-pixel A4, though the whitesub-pixel A4 consumes electric current most among the four colorsub-pixels in the long run and on the average whereas the whitesub-pixel has the high luminous efficiency and the small maximumelectric current value. In other words, this makes it possible to extendthe life span of the organic EL display device 10 in the case of each ofthe embodiments. A ratio of the white sub-pixel A4 to each of the othercolor sub-pixels in area of the opening portion may be determineddepending on color distribution in a displayed videos and properties ofthe materials. It is desirable that the ratio should be not smaller than1.1:1.0. It is more desirable that the ratio should be not smaller than2.0:1.0.

Fourth Embodiment

Descriptions will be provided for a fourth embodiment of the presentinvention. FIGS. 6 and 7 respectively show examples of a pixel layout inan active matrix display device. In each of the pixel layouts shown inFIGS. 6 and 7, sub-pixels in each two neighboring rows are arranged in away that sub-pixels for any one color in one row slide away fromsub-pixels for the same color in the other row. In the case where videosare intended to be expressed by use of the four colors, not only thepixel layout as shown in FIG. 6 but also the pixel layout as showingFIG. 7 is conceivable. In the case of the pixel layout shown in FIG. 6,sub-pixels for any one color in one of each two neighboring rows slideaway from sub-pixels for the same color in the other of the twoneighboring rows by a distance 1.5 times the width of each of thesub-pixels. In the case of the pixel layout shown in FIG. 7, sub-pixelsfor any one color in one of each two neighboring rows slide away fromsub-pixels for the same color in the other of the two neighboring rowsby a distance twice the width of each of the sub-pixels. In the case ofthese pixel layouts, sub-pixels for each of the four colors areuniformly distributed and thus arranged. Accordingly, these pixellayouts are advantageous in the case where natural images and movingpictures are intended to be displayed.

In the case of any one of the two layouts, for the purpose of reducingload imposed on external integrated circuits (ICs) for controlling theorganic EL display device 10, it is desirable that, as far as sub-pixelsfor any one color, for example, sub-pixels for red 1 are concerned, adata signal to the sub-pixels should be sent from one data line DL1shown in FIG. 6 or 7. As a result, the layout needs to be designed in away that its panel includes a data line DL1 which are bent to a largeextent as shown by a bold line in FIG. 6 or 7. This is because, in thecase of the pixel layout shown in FIG. 6, sub-pixels for red 1 in anyone row slide away from sub-pixels for red 1 in the subsequent row by adistance 1.5 times the width of each of the sub-pixels. In addition,this is because, in the case of the pixel layout shown in FIG. 7,sub-pixels for red 1 in any one row slide away from sub-pixels for red 1in the subsequent row by a distance twice the width of each of thesub-pixels.

The present inventors have found that, in a case where, out of the foursub-pixels constituting one pixel in each of such pixel layouts, twosub-pixels have the same horizontal pitches, the following contrivanceenables a rational layout design. In accordance with this contrivance,sub-pixels arranged in any one row are designed to have layouts,including wires, which are obtained by horizontally reversing layouts ofcorresponding sub-pixels arranged in the following row. This alternationmakes it possible to make a length, in which each data lines DL1 bendswhen the data line DL1 goes from one row to the subsequent row, equal toa length, in which the data line DL1 bends when the data line DL1 goesfrom another row to the subsequent row. In addition, this alternationmakes it possible to make a length, in which each power supply linePVDD1 bends when the power supply line PVDD1 goes from one row to thesubsequent row, equal to a length, in which the power supply line PVDD1bends when the power supply line PVDD1 goes from another row to thesubsequent row.

Detailed descriptions will be provided for the fourth embodiment of thepresent invention with reference to the related drawings. FIG. 8 is aschematic diagram showing a case where the sub-pixels with the ratioamong the areas of the opening portions thereof according to the thirdembodiment, which have been shown in FIG. 5, are laid out as shown inFIG. 7. Sub-pixels A1 to A4 shown in FIG. 8 correspond to the sub-pixelsA1 to A4 shown in FIG. 5. In FIG. 8, the sub-pixels are laid out in thesequence of a red, blue, green to white sub-pixels. The pixel layoutshown in FIG. 8 is different from the pixel layout shown in FIG. 5 inthis color sequence.

In FIG. 8, the horizontal pitches of the sub-pixels A1 and A2 aredenoted by a2; the horizontal pitch of the sub-pixel A3, a1; and thehorizontal pitch of the sub-pixel A4, a3. In addition, an amount ofshift of a sub-pixel for one color in one of each two neighboring rowsfrom a sub-pixel for the same color in the other of the two neighboringrows is denoted by s. In this case, with regard to the (n−1)th row, alength in which a data line DL1 bends in a sub-pixel A1 is expressed bys-a2; a length in which a data line DL1 bends in a sub-pixel A3, s-a1; alength in which a data line DL1 bends in a sub-pixel A2, s-a2; and alength in which a data line DL1 bends in a sub-pixel A4, s-a3.Furthermore, with regard to the (n−1)th row, a length in which a powersupply line PVDD1 bends in a sub-pixel A1 is expressed by s-a1-a2; alength in which a power supply line PVDD1 bends in a sub-pixel A3,s-a1-a2; a length in which a power supply line PVDD1 bends in asub-pixel A2, s-a2-a3; and a length in which a power supply line PVDD1bends in a sub-pixel A4, s-a2-a3. With regard to the nth row, a lengthin which a data line DL1 bends in a sub-pixel A1 is expressed by s-a2; alength in which a data line DL1 bends in a sub-pixel A3, s-a1; a lengthin which a data line DL1 bends in a sub-pixel A2, s-a2; and a length inwhich a data line DL1 bends in a sub-pixel A4, s-a3. Furthermore, withregard to the nth row, a length in which a power supply line PVDD1 bendsin a sub-pixel A1 is expressed by s-a2-a3; a length in which a powersupply line PVDD1 bends in a sub-pixel A3, s-a1-a2; a length in which apower supply line PVDD1 bends in a sub-pixel A2, s-a1-a2; and a lengthin which a power supply line PVDD1 bends in a sub-pixel A4, s-a2-a3.

The length in which the data line DL1 bends in the sub-pixel A3 in the(n−1)th row is equal to the length in which the data line DL1 bends inthe sub-pixel A3 in the nth row. The length in which the data line DL1bends in the sub-pixel A4 in the (n−1)th row is equal to the length inwhich the data line DL1 bends in the sub-pixel A4 in the nth row. Thelength in which the power supply line PVDD1 bends in the sub-pixel A3 inthe (n−1)th row is equal to the length in which the power supply linePVDD1 bends in the sub-pixel A3 in the nth row. The length in which thepower supply line PVDD1 bends in the sub-pixel A4 in the (n−1)th row isequal to the length in which the power supply line PVDD1 bends in thesub-pixel A4 in the nth row. For this reason, a pixel layout obtained byhorizontally reversing a pixel layout used in the (n−1)th row can beused as the pixel layout for the nth row without any other modification.In contrast, the length in which the power supply line PVDD1 bends inthe sub-pixel A1 in the (n−1)th row is different from the length inwhich the power supply line PVDD1 bends in the sub-pixel A1 in the nthrow. In addition, the length in which the power supply line PVDD1 bendsin the sub-pixel A2 in the (n−1)th row is different from the length inwhich the power supply line PVDD1 bends in the sub-pixel A2 in the nthrow. However, the pixel layout of the sub-pixel A1 and the pixel layoutof the sub-pixel A2 is similar to each other. For this reason, thesub-pixels A1 and A2 can be arranged in the nth row in the followingmanner: layouts obtained by horizontally reversing the layouts of thesub-pixels A1 in the (n−1)th row can be used as the layouts of thesub-pixels A2 in the nth row, and layouts obtained by horizontallyreversing the layouts of the sub-pixels A2 in the (n−1)th row can beused as the layouts of the sub-pixels A1 in the nth row. In other words,when a total of four patterns consisting of one layout pattern for eachof the sub-pixels A1, A2, A3 and A4 is prepared, the pixel layout shownin FIG. 9 can be designed as in the case of the pixel layout shown inFIG. 7.

In the case of the layout where the arrangement of the color sub-pixelsin one of each two neighboring rows shifts from the arrangement of thecolor sub-pixels in the other of the two neighboring rows as shown inFIGS. 6 and 7, the number of pixel layout patterns can be held down bysatisfying the following two conditions at a time. A first condition isthat, out of the four color sub-pixels, at least two color sub-pixelshave the same layout. A second condition is that the sub-pixels havingthe same layout are arranged in a way that the sub-pixels are not nextto each other. Holding down the number of pixel layout patterns makes itpossible to reduce a load imposed on layout design. This technique canbe applied to not only organic EL display devices but also liquidcrystal display devices.

Fifth Embodiment

Descriptions will be provided for a fifth embodiment of the presentinvention. FIG. 9 is a diagram showing a case where sub-pixels with theratio among the areas of the opening portions thereof according to thefirst embodiment, which have been shown in FIG. 1, are laid out as shownin FIG. 7. Sub-pixels A1 to A4 shown in FIG. 9 correspond to thesub-pixels A1 to A4 shown in FIG. 1. In FIG. 8, the sub-pixels are laidout in the sequence of a red, blue, green to white sub-pixels. The pixellayout shown in FIG. 9 is different from the pixel layout shown in FIG.5 in this color sequence.

In FIG. 9, the horizontal pitches of the sub-pixels A1, A2 and A3 aredenoted by a1; and the horizontal pitch of the sub-pixel A4, a2. Inaddition, an amount of shift of a sub-pixel for one color in one of eachtwo neighboring rows from a sub-pixel for the same color in the other ofthe two neighboring rows is denoted by s. In this case, with regard tothe (n−1)th row, a length in which a data line DL1 bends in a sub-pixelA1 is expressed by s-a1; a length in which a data line DL1 bends in asub-pixel A2, s-a1; a length in which a data line DL1 bends in asub-pixel A3, s-a1; and a length in which a data line DL1 bends in asub-pixel A4, s-a2. Furthermore, with regard to the (n−1)th row, alength in which a power supply line PVDD1 bends in a sub-pixel A1 isexpressed by s-2*a1; a length in which a power supply line PVDD1 bendsin a sub-pixel A2, s-2*a1; a length in which a power supply line PVDD1bends in a sub-pixel A3, s-a1-a2; and a length in which a power supplyline PVDD1 bends in a sub-pixel A4, s-a1-a2. With regard to the nth row,a length in which a data line DL1 bends in a sub-pixel A1 is expressedby s-a1; a length in which a data line DL1 bends in a sub-pixel A2,s-a1; a length in which a data line DL1 bends in a sub-pixel A3, s-a1;and a length in which a data line DL1 bends in a sub-pixel A4, s-a2.Furthermore, with regard to the nth row, a length in which a powersupply line PVDD1 bends in a sub-pixel A1 is expressed by s-a1-a2; alength in which a power supply line PVDD1 bends in a sub-pixel A2,s-2*a1; a length in which a power supply line PVDD1 bends in a sub-pixelA3, s-2*a1; and a length in which a power supply line PVDD1 bends in asub-pixel A4, s-a1-a2.

The length in which the power supply line PVDD1 bends in the sub-pixelA2 in the (n−1)th row is equal to the length in which the power supplyline PVDD1 bends in the sub-pixel A2 in the nth row. The length in whichthe power supply line PVDD1 bends in the sub-pixel A4 in the (n−1)th rowis equal to the length in which the power supply line PVDD1 bends in thesub-pixel A4 in the nth row. For this reason, a pixel layout obtained byhorizontally reversing a pixel layout used in the (n−1)th row can beused as the pixel layout for the nth row without any other modification.In contrast, the length in which the power supply line PVDD1 bends inthe sub-pixel A1 in the (n−1)th row is different from the length inwhich the power supply line PVDD1 bends in the sub-pixel A1 in the nthrow. In addition, the length in which the power supply line PVDD1 bendsin the sub-pixel A3 in the (n−1)th row is different from the length inwhich the power supply line PVDD1 bends in the sub-pixel A3 in the nthrow. However, the pixel layout of the sub-pixel A1 and the pixel layoutof the sub-pixel A2 is similar to each other. For this reason, thesub-pixels A1 and A3 can be arranged in the nth row in the followingmanner: layouts obtained by horizontally reversing the layouts of thesub-pixels A1 in the (n−1)th row can be used as the layouts of thesub-pixels A3 in the nth row, and layouts obtained by horizontallyreversing the layouts of the sub-pixels A3 in the (n−1)th row can beused as the layouts of the sub-pixels A1 in the nth row. Furthermore,the pixel layouts of the sub-pixels A1, A2 and A3 are similar to oneanother. A layout for a sub-pixel which causes the power supply linePVDD1 to bend with a length expressed by s-2*a1 can be used commonly forsub-pixels A1, A2 and A3. In other words, when a total of three patternsis prepared for layouts of the sub-pixels A1, A2, A3 and A4, the pixellayout shown in FIG. 9 can be designed as in the case of the pixellayout shown in FIG. 7.

In this manner, the horizontal pitches of two sub-pixels which are notnext to each other are equal to each other, even in the case where thehorizontal pitches of three sub-pixels are equal to one another as inthe case of this embodiment. As a result, the number of pixel layoutpatterns can be held down, and accordingly a load imposed on layoutdesign can be reduced, as in the case of the fourth embodiment.

It should be noted that, with regard to the pixel layout shown in FIG.7, sub-pixels for any one color in one of each two neighboring rowsslide away from sub-pixels for the same color in the other of the twoneighboring rows by a distance two times the width of each of thesub-pixels. In the case where videos are intended to be expressed by useof the four colors, the shift of sub-pixels for the same color betweeneach two neighboring rows by a distance two times the width of each ofthe sub-pixels means the shift of pixel components between each twoneighboring rows by a distance a half times a horizontal pitch of eachof the pixel components. This is because each pixel component includesthe four sub-pixels. In other words, in the case of the layout shown inFIG. 7, image components next to each other in the vertical directionare laid out in a way that the image components slide from imagecomponents next to each other in the vertical direction in the other ofthe two neighboring rows by a distance a half times a horizontal pitchof each of the image components. Thereby, sub-pixels for each of thefour colors are laid out homogeneously in the display screen. In a casewhere sub-pixels for each of the four colors are laid outinhomogeneously in the display screen, an unsatisfactory condition maytake place. Examples of the unsatisfactory condition include a conditionin which, when an video expressed with a single color is displayed, theimage looks like streaks as a consequence of lighting only sub-pixelsfor the single color. However, the layout shown in FIG. 7 can reduceoccurrence of such an unsatisfactory condition stemming from the layout.That is because sub-pixels for each of the four colors are laid outhomogeneously in the display screen. In the case of the pixel layoutdisclosed in Japanese Patent Laid-open Official Gazette No. 2004-334204,each four color sub-pixels are laid out as a 2×2 matrix, but this typeof pixel layout is disadvantageous for displaying moving pictures andthe like. That is because only two color sub-pixels are present in thehorizontal direction in each 2′2 matrix. In the case of the pixel layoutshown in FIG. 7, sub-pixels for each of the four colors are laid outhomogeneously in the display screen. Accordingly, this makes it possibleto improve visibility of the display device.

Moreover, for the purpose of improving apparent resolution in thehorizontal direction, in some cases, original video signals are sampledin timings which are different in sub-pixels from one color to another.In a case where this technique is applied to the pixel layouts shown inFIGS. 6 and 7, clock signals for sampling video signals need to be readyin a way that clock signals used in odd-numbered rows and clock signalsused in even-numbered rows are different from each other. In the case ofthe layout shown in FIG. 7, however, sub-pixels are laid out in a waythat the horizontal pitches of image components in any one of theodd-numbered rows slides away from the horizontal pitches of imagecomponents in an even-numbered row subsequent to the odd-numbered row bythe distance a half times each of the horizontal pitches. For thisreason, it suffices that clock signals are generated in a way thatphases of clock signals for the odd-numbered rows shift from phases ofclock signals for the even-numbered rows by 180°. Thus, one type ofclock signals can be easily generated from the other type of clocksignals. Accordingly, this makes it easy to design the external drivingcircuit. In this regard, the layout shown in FIG. 7 is advantageous aswell.

Other Embodiments

Various modifications will become possible for those skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

1. A display device comprising: a plurality of sub-pixels configured todisplay a plurality of colors including white, each of the sub-pixelsincluding: a self-luminous element configured to emit light by receivingsupply of electric current; an input unit configured to input aluminance signal for determining luminance of the self-luminous elementinto the sub-pixel; and a control unit configured to control the supplyof electric current to the self-luminous element, wherein an area oflight emission in each of the sub-pixels for the white is larger than anarea of light emission in each of the sub-pixels for the other colors.2. The display device of claim 1, wherein the displayed colors are fourcolors of blue, green, red, and white.
 3. The display device of claim 1,wherein a ratio among the sub-pixels for each of the colors in an areaof light emission is set up in accordance with a ratio among substantialelectric currents supplied to the self-luminous elements for each of thecolors.
 4. The display device according to claim 3, wherein the ratioamong the electric currents is calculated from averages of electriccurrents supplied to the self-luminous elements when a plurality ofimages are displayed on the display device.
 5. The display device ofclaim 1, wherein a color emitted by the self-luminous element is thewhite, and wherein the other displayed colors are obtained by convertingthe white to the displayed colors except for the white by use of colorfilters.
 6. The display device of claim 1, wherein the self-luminouselement is an organic electroluminescent element.
 7. A display devicecomprising: a plurality of sub-pixels arranged in horizontal direction,and configured to display a plurality of colors, and to constitute animage component, each of the sub-pixels including: a self-luminouselement configured to emit light by receiving supply of electriccurrent; an input unit configured to input a luminance signal fordetermining luminance of the self-luminous element into the sub-pixel;and a control unit configured to control the supply of electric currentto the self-luminous element, wherein at least two sub-pixels of thesub-pixels have an equal horizontal pitch.
 8. The display device ofclaim 7, wherein at least two sub-pixels of the sub-pixels, which arenot next to each other, have an equal horizontal pitch.
 9. The displaydevice of claim 7, wherein sub-pixels for any one of the colors arearranged in a way that the sub-pixels for the same color are not next toeach other.
 10. The display device of claim 7, wherein a color emittedby the self-luminous element is the white, and wherein the otherdisplayed colors are obtained by converting the white to the displayedcolors except for the white by use of color filters.
 11. The displaydevice of claim 7, wherein the self-luminous element is an organicelectroluminescent element.
 12. A display device comprising: a pluralityof sub-pixels arranged in horizontal direction, and configured todisplay a plurality of colors, and to constitute an image component,each of the sub-pixels including: a self-luminous element configured toemit light by receiving supply of electric current; an input unitconfigured to input a luminance signal for determining luminance of theself-luminous element into the sub-pixel; and a control unit configuredto control the supply of electric current to the self-luminous element,wherein image components next to each other in vertical direction arearranged in a way that one of the image components shifts from the otherof the image components by a distance equal to a half of a horizontalpitch of each of the image components.
 13. The display device of claim12, wherein a color emitted by the self-luminous element is the white,and wherein the other displayed colors are obtained by converting thewhite to the displayed colors except for the white by use of colorfilters.
 14. The display device of claim 12, wherein the self-luminouselement is an organic electroluminescent element.